When an electronic device operates, the electronic components on the printed circuit board thereof may generate energy in the form of heat, which is readily accumulated around the circuit board and difficult to dissipate away. If no proper heat-dissipating mechanism is provided to transfer enough heat to the ambient air, the elevated operating temperature may result in damage of the electronic components, a breakdown of the whole electronic device or reduced operation efficiency. Therefore, it is important to dissipate the heat generated from the electronic components in order to stabilize the operation and extend the operational life of the electronic device.
For example, a heat sink is fixed onto a surface of the circuit board of a power supply apparatus. By means of the heat sink, the heat generated from the electronic components on the circuit board is transferred to the ambient air. Since the heat sink is developed toward increased heat transfer area and reduced thermal resistance, it is important to provide a process of assembling the heat sink in a simplified manner.
Referring to FIG. 1(a), a schematic layout configuration of a circuit board within a conventional power supply apparatus is illustrated. As shown in FIG. 1(a), the circuit board 10 includes a first surface 10a and a second surface 10b, which are opposed to each other. Several electronic components 11 are mounted on the first surface 10a of the circuit board 10. The electronic components 11 include for example at least a transistor, at least a resistor, at least a capacitor, at least a diode, at least a magnetic elements and the like. The power converting circuit cooperatively defined by these electronic components 11 and the trace pattern of the circuit board 10 is responsible for power conversion. In addition, at least one heat sink 12 is fixed on the first surface 10a of the circuit board 10 for dissipating heat generated from the electronic components 11. For increasing heat transfer area and reducing thermal resistance, the heat sink 12 is an aluminum extrusion element having an L-shaped or T-shaped cross-section. Take an L-shaped cross-sectional heat sink 12 for example. The heat sink 12 principally comprises a first part 121 and a second part 122, which are perpendicular to each other. The first part 121 of the heat sink 12 is supported on the first surface 10a of the circuit board 10. The second part 122 of the heat sink 12 is extended from the upper edge of the first part 121 and substantially parallel with the circuit board 10 such that a space 13 is formed between the second part 122 and the circuit board 10. Some high power electronic components 11, e.g. transistors, may be fastened onto the first part 121 of the heat sink 12 in order to increase heat-dissipating efficiency.
Please refer to FIG. 1(b), which is a partial schematic cross-sectional view of the circuit board shown in FIG. 1(a). The circuit board 10 has a perforation 10c. The bottom 123 of the first part 121 of the heat sink 12 has a groove 124 corresponding to the perforation 10c of the circuit board 10. The groove 124 and the perforation 10c have inner threads formed on the inner wall thereof. For coupling the heat sink 12 with the circuit board 10, a screw 14 is penetrated through the perforation 10c of the circuit board 10 and then screwed in the groove 124 such that the external thread of the screw 14 is engaged with the inner thread of the groove 124. The pins 11a of the high power electronic components 11, which are fastened onto the first part 121 of the heat sink 12, are inserted into corresponding via holes 10d of the circuit board 10. After the molten solder paste is applied on the peripheries of these via holes 10d, the pins 11a are welded onto the circuit board 10. Since the heat sink 12 is an aluminum extrusion element having an L-shaped or T-shaped cross-section, the center of gravity of the heat sink 12 is shifted from the center line thereof. In other works, the heat sink 12 fails to be firmly secured onto the circuit board 10 by screwing into the groove and welding the pins. If the power supply apparatus is suffered from a drop or a strong impact, shear stresses may be exerted on the contact portions between the screw 14 and the circuit board 10 and/or between the pins 11a and the circuit board 10. Due to these shear stresses, the heat sink 12 is readily detached from the circuit board 10.
Hereinafter, a process of fixing the heat sink on the circuit board will be illustrated with reference to FIG. 2 and also FIGS. 1(a) and 1(b). Firstly, a circuit board 10 including a first surface 10a and a second surface 10b is provided (Step S11). Then, the circuit board 10 is turned over. A screw 14 is penetrated through the perforation 10c of the circuit board 10 and then screwed in the groove 124 of the first part 121 of the heat sink 12 such that the external thread of the screw 14 is engaged with the inner thread of the groove 124, thereby fixing the heat sink 12 on the circuit board 10 (Step S12). The circuit board 10 is turned back. Then, several electronic components 11 constituting a power converting circuit are disposed on the first surface 10a of the circuit board 10 such that a space 13 is formed between the second part 122 and the circuit board 10 (Step S13). Afterwards, these electronic components 11 and the circuit board 10 are heated in a reflow furnace to melt the solder paste. The circuit board 10 is then cooled to solidify the solder paste so as to bond the electronic components 11 onto the circuit board 10 (Step S14). Since the space 13 between the second part 122 of the heat sink 12 and the circuit board 10 becomes hindrance from mounting the electronic components 11, this assembling process is time-consuming and troublesome.
Hereinafter, another process of fixing the heat sink on the circuit board will be illustrated with reference to FIG. 3 and also FIGS. 1(a) and 1(b). Firstly, a circuit board 10 including a first surface 10a and a second surface 10b is provided (Step S21). Then, several electronic components 11 constituting a power converting circuit are disposed on the first surface 10a of the circuit board 10, and these electronic components 11 and the circuit board 10 are heated in a reflow furnace to melt the solder paste so as to bond the electronic components 11 onto the circuit board 10 (Step S22). Then, the circuit board 10 is turned over. A screw 14 is penetrated through the perforation 10c of the circuit board 10 and then screwed in the groove 124 of the first part 121 of the heat sink 12 such that the external thread of the screw 14 is engaged with the inner thread of the groove 124, thereby fixing the heat sink 12 on the circuit board 10 (Step S23). The circuit board 10 is turned back. Afterwards, the pins 11a of the high power electronic components 11 are inserted into corresponding via holes 10d of the circuit board 10 and then the main bodies of the high power electronic components 11 are fastened onto the first part 121 of the heat sink 12. Then, these electronic components 11 and the circuit board 10 are heated in the reflow furnace again so as to bond the pins 11a onto the circuit board 10 (Step S24). As known, the procedures of turning over and turning back the circuit board 10 are troublesome. In addition, the procedures of successively inserting the pins 124b into these via holes 10d are labor-intensive and time-consuming.
In views of the above-described disadvantages resulted from the prior art, the applicant keeps on carving unflaggingly to develop a heat sink fastening device for facilitating fixing a heat sink on a circuit board according to the present invention through wholehearted experience and research.